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Alkaline solutions (Opponents of acids) are liquids which consume acids.
Left: Sodium is an alkali metal.
Photo 2: It reacts vigorously (not only in water but also) in red cherry juice:
Photo 3: It melts forming a silvery ball which runs on the surface and finally dissolves. The red colour changes to green. This alkaline solution is sodium hydroxide solution, a the most common compound of the alkali sodium.
Right: Sodium hydroxide solution is a  strong Alkali. It consumes a lot of citric acid while the colour of the indicator returns to red.